The present invention relates to cushion sheets used in, for example, seat covers that cover seats of vehicles, and manufacturing methods for the cushion sheets.
Conventionally, a seat cover 31 as in FIG. 6 having three layers, for example, is used as a seat cover for covering a seat of a vehicle. More specifically, the seat cover 31 includes a fibrous sheet 32, a cushion sheet 33 bonded with the backside of the fibrous sheet 32, and a back lining 34 bonded with the backside of the cushion sheet 33. The fibrous sheet 32 is formed by, for example, a fabric or a vinyl chloride sheet. The cushion sheet 33 is formed of, for example, soft urethane foam. The back lining 34 is formed of, for example tricot or unwoven fabric.
The back lining 34 improves the smoothness of the backside of the cushion sheet 33, thus making it easy to sew the seat cover 31 and install the seat cover 31 in the cushion body of the seat of the vehicle.
However, for forming the seat cover 31, the back lining 34 is bonded with the entire backside of the cushion sheet 33 through, for example, frame laminating. This decreases the air permeability of the seat cover 31. Further, the fibrous sheet 32 and the cushion sheet 33 exhibit a different extension rate than the extension rate of the back lining 34. Thus, when the seat cover 31 is secured to the cushion body, wrinkles tend to be caused in the seat cover 31. Also, the frame laminating for bonding the back lining 34 with the backside of the cushion sheet 33 increases the steps for manufacturing the cushion sheet 33, complicating the manufacture of the cushion sheet 33. The cost for manufacturing the cushion sheet 33 is thus raised.
To solve these problems, for example, Japanese Laid-Open Patent Publication No. 2000-107471 proposes a cushion sheet 35, which is shown in FIG. 7. The cushion sheet 35, referring to the drawing, includes an air-permeable sheet material 36. A plurality of adhesive layers 38, or dots of adhesive, are formed on the backside of the air-permeable sheet material 36. The adhesive layers 38 are provided by applying hot-melt adhesives 37 on the backside of the air-permeable sheet material 36 in accordance with a dotted pattern. More specifically, the hot-melt adhesives 37 are extruded through a T die in a molten state and applied on the backside of the air-permeable sheet material 36 in such a manner as to form a prescribed pattern. This provides the adhesive layers 38 that are arranged in accordance with the dotted pattern. This ensures the air permeability of the cushion sheet 35 and the smoothness of the cushion sheet 35 that is comparable with that of the back lining 34 of the seat cover 31 of FIG. 6.
To form the cushion sheet 35, the adhesive layers 38 must be arranged in accordance with the prescribed dotted pattern. The speed for applying the hot-melt adhesives 37 is thus restricted to a certain level. If such speed is excessively increased, the dots cannot be arranged in a desired manner. This makes it impossible to ensure a necessary smoothness of the cushion sheet 35, hampering sewing of the seat cover 31.
Each dot of the dotted pattern, which is formed on the air-permeable sheet material 36 by the hot-melt adhesives 37, focally contains a relatively great amount of adhesive. This causes the adhesives 37 to permeate through the air-permeable sheet material 36. In this state, the hot-melt adhesives 37 do not contribute to improvement of the smoothness of the backside of the cushion sheet 35. If the quantity of such adhesives 37 increases, an increased amount of adhesive becomes necessary for forming the adhesive layers 38. This increases the manufacturing cost of the cushion sheet 35. Further, permeation of the hot-melt adhesives 37 hardens the air-permeable sheet material 36. This degrades the feel of the cushion sheet 35 and lowers the air permeability of the cushion sheet 35.